The p,p'-disubstituted .alpha.-trichloromethylbenzylphenyl ethers of the present invention are a novel class of compounds. Their properties are such that they exhibit utilities as selective or nonselective insecticides and/or larvicides. In addition, many of the members of the class of compounds of the present invention also exhibit properties of biodegradability. In view of the fact that DDT [1, 1, 1 trichloro-2,2-bis(p-chlorophenyl)ethane], the insecticide in most widespread use today, is not biodegradable, these properties take on added importance by serving to minimize one of the greatest deficiencies of prior art insecticides.
There is growing concern about the continuing liberation of vast quantities of DDT into the environment. The very qualities which make DDT such an effective contact or residual insecticide, i.e., its very low water solubility and high lipid solubility, caused by the non-polarity of the DDT molecule, result in its accumulation in the fatty or lipid tissues of animals. These properties result in ever increasing concentrations in the tissues of carnivorous animals at the upper ends of food chains. The problems associated with this magnification phenomenon are further intensified by the enzymatic metabolic conversion of DDT to the even more stable dehydrochlorination product, DDE [1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene].
Drug metabolizing enzymes, known as multifunction oxidases (MFO), which play a dominant role in detoxifying insecticides in both insects and higher animals, such as birds, fish, and mammals do not function on DDT and its metabolic derivatives DDE and DDD (or TDE) [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane] as substrates. This single factor accounts for their storage and accumulation in animal tissues, especially at the higher ends of food chains.
Certain known symmetrical DDT analogs, such as methoxychlor [1,1,1-trichloro-,2,2-bis(p-methoxyphenyl)ethane] and methiochlor [1,1,1-trichloro-2,2-bis-(p-methiophenyl) ethane] are readily attacked by MFO enzymes, which metabolically convert or boidegrade such analogs into environmentally acceptable products which are rapidly eliminated by animals. Thus, methoxychlor is an example of a biodegradable insecticide which is not generally accumulated in animal tissues and is, thus, a more prudent choice than DDT for a variety of uses where environmental pollution is an important factor. However, metoxychlor and other known symmetrical DDT analogs (e.g., methylchlor [1,1,1-trichloro-2,2-bis(p-methylphenyl)ethane] and methiochlor), while exhibiting satisfactory insecticidal activity towards certain species of insects, exhibit considerably less insecticidal activity than DDT towards other species of insects.
One attempt to remedy the problems of the prior art is disclosed in the copending application of Metcalf et al., "Insecticidal Biodegradable Analogues of DDT," Ser. No. 147,241, filed May 26, 1971, and having a common assignee with the present application. These asymmetrical analogues of DDT have in general proved to be biodegradable and effective as insecticides. The compounds in accordance with the present invention, however, offer a mechanism of molecular cleavage of the -O-CH(CCl.sub. 3)-bonds, whereby biodegradability may be increased. In addition to biodegradability, certain of the compounds of the present invention offer outstanding toxicity as either selective or non-selective insecticides. The compounds of the present invention are further distinguished from prior art insecticides in that they breakdown upon prolonged exposure to sunlight, which would prove to be beneficial in applications where persistence of the insecticide is either not necessary or undesirable.